The use of fluorine-containing compounds in preparing coatings having a slippery outer surface is known in the art. By way of illustration, European Patent Application publication No. 480,089, published on Apr. 15, 1992 discloses the reaction of isophorone diisocyanate ("IPDI") with a fluorine-containing monoalcohol ("monol") in order to prepare a fluoro-modified urethane for use as a resin modifier by grafting onto a fluoroolefin-vinyl ether copolymer resin. The modified resin was subsequently used in accordance with the disclosures of the '089 publication to modify a coating composition comprising the modified resin having a 50% solids content, and coated substrates were prepared and their physical properties measured. The '089 publication also discloses, at page 12 thereof, a "wish-list" of conventional film-forming resins suitable for use in combination with the modified resin in coating compositions, including polyurethane resins.
The use of moisture-curable one-component and two-component isocyanate-based coating compositions in the production of coatings for substrates is also known in the art. As an illustration of a one-component system, U.S. Pat. No. 4,456,658 discloses a process for coating polyvinyl chloride sheet products with a moisture-curable, clear coating comprising a binder which consists essentially of at least one polyisocyanate which is liquid at room temperature. The polyisocyanate binder is further characterized at column 2, lines 12-17 of the '658 patent as being in particular polyisocyanates containing biuret or isocyanurate groups and optionally uretidione groups and having an average isocyanate functionality above 2, preferably from about 2.5 to 6. Unfortunately, the '658 patent is limited to coating polyvinyl chloride sheet products, which represents a narrow market niche as compared to the wide variety of substrates in the marketplace that could benefit from a suitable one-component coating. The coating compositions of the examples of the '658 patent also have the disadvantage of slow drying times when cured with atmospheric moisture at room temperature.
As an additional illustration, U.S. Pat. No. 4,292,350 discloses a process of coating substrates comprising applying to the substrate a moisture-curable, solvent-free or low solvent lacquer composition containing as a binder an isocyanate mixture. The isocyanate mixture described in the '350 patent is a mixture of (a) an organic polyisocyanate having an average isocyanate functionality of greater than 2 which contains biuret, urethane and/or isocyanurate groups and has an isocyanate content of from about 13 to 30% by weight, and (b) at least one monoisocyanate having a defined structure. The monoisocyanate is further described at column 3, lines 18-22 of the '350 patent as being suitably prepared by reacting excess quantities of a diisocyanate with a hydrocarbon-containing hydroxyl compound, followed by removal of unreacted excess diisocyanate by distillation using, for example, a thin layer evaporator. The process of this patent is more cumbersome than might be desired, particularly in regard to the need for the isocyanate mixture and the need for removal of excess diisocyanate from the prepared monoisocyanate component.
Conventional methods for the heat-curing of monomeric diisocyanates have frequently posed toxicity concerns that are typically associated with employee exposure by the end user to volatile monomeric diisocyanates.
Recent efforts have been made to overcome these toxicity concerns; however, other problems tend to occur. By way of illustration, U.S. Pat. No. 5,144,031 discloses both heat-crosslinkable, one-component blocked-isocyanate compositions and two-component coating compositions which are said to harden at room temperature or at a slightly elevated temperature. The coating compositions of the '031 patent contain isocyanurate group-containing polyisocyanates produced by the steps of: (a) partially trimerizing the isocyanate groups of a cycloaliphatic diisocyanate in the presence of a trimerization catalyst and optionally in the presence of an inert solvent, (b) terminating the trimerization reaction at the desired degree of trimerization, (c) removing unreacted starting diisocyanate and any other volatile constituents, and (d) prior to step (c), adding 1 to 30 % by weight of a monohydric alcohol being an ester alcohol, based upon the weight of the diisocyanate. Unfortunately, this process is more complicated than might be desired, particularly with the requirement for the step (c) removal of unreacted starting diisocyanate after addition of the monohydric alcohol. In addition, the presence of the ester alcohol necessitates that a urethanization reaction takes place at the site of the ester alcohol on the prepolymer, in addition to the trimerization reaction that takes place with respect to the isocyanate moieties, rendering a more complex reaction sequence than might be desired.
Recently, new processes for providing low VOC one-component and two-component heat or moisture curable urethane coatings based on organic polyisocyanates, and advantageously employing dimers, trimers, or biurets of aliphatic diisocyanates, have been disclosed, for example, in commonly-assigned, co-pending U.S. application Ser. Nos. 08/065,005 (filed on May 24, 1993 and claiming low VOC, 1-K moisture curable coating compositions), 08/064,996 (filed on May 24, 1993 and claiming low VOC, 2-K moisture curable coating compositions), and 08/065,009 (filed on May 24, 1993 and claiming low VOC, 1-K and 2-K heat curable coating compositions). The processes disclosed in these copending applications, although useful for coating a wide variety of substrates, not limited to the polyvinyl chloride substrate of the '658 patent and not employing the isocyanate mixture of the '350 patent, have the disadvantage of not always providing as "slippery" a coating as otherwise might be desired in use, for example, as an automotive top-coat, clear-finish coating. Accordingly, new coating compositions and processes providing the desired slipperiness characteristics for the coating's outer surface, without compromising good substrate adhesion characteristics between the coating and the underlying substrate, would be highly desired by the coatings manufacturing community. The present invention provides one solution to this industry need. The present invention also provides a solution to the toxicity problem that can be associated with monomeric diisocyanates by employing a low toxicity coating composition that is also low in VOC.